Particle Motion & Wave Propagation Flashcards by Amber Verbeek

What are the 5 steps of a sonographers job?

1- operator control 
2- transducer activation (sending)
3- sound interaction 
4- transducer activation (receiving) 
5- image display

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Describe operators control

Operator (sonographer) decides which transducer and preset to use based on requisition and patient history

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Describe transducer activation (sending)

Electrical current is sent to transducer and converted into sound through “reverse piezoelectric effect”

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Describe sound interaction

Sound waves travel through tissue and produce echos that return to transducer

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Describe transducer activation (receiving)

Returning sound waves are converted back into electrical current through “piezoelectric effect”

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Describe image display

Electrical current is processed through the machine and converted into an image on a monitor

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What is the Piezoelectric effect

Pressure waves are applied to certain crystals which produce electrical pulses (voltage)

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What is the reverse piezoelectric effect

When electrical pulses (voltage) are applied to certain crystals which produce sound waves

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What is Attenuation

Weakening of sound waves

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What is Acoustic

Refers to sound

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What is propagation

Refers to travel

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What is acoustic propagation

Refers to the effects tissues cause on sound

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What are bioeffects

Refers to the effects of ultrasound on tissue

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Is sound a propagating variation (a wave)

Yes

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Do waves carry matter or energy ?

Energy

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What type of wave needs a medium to travel?

Mechanical wave

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What are the qualities of waves called?

Variables

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What are the 4 acoustic variables of sound when it travels through a medium?

1- pressure
2- density
3- particle motion
4- temperature

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How can pressure be expressed on a sine wave?

Crests - increased pressure

Troughs - decreased pressure

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In regards to pressure, when particles vibrate when is there high pressure, when is there low pressure?

High pressure - when particles are close together

Low pressure - when particles are farther apart

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What is density ?

Density is the concentration of particles or mass per unit volume

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Regions of low density are called?

Rarefactions

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Regions of high density are called?

Compressions

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List the two parts of temperature related to sound

Sound is an energy

Energy creates heat

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Sound is what type of wave?

A mechanical wave | needs a medium to travel through, can’t travel through space

List some types of mechanical waves

Sound Transverse Rayleigh Longitudinal

List some types of NON mechanical waves

Gamma rays X rays Light

Describe longitudinal waves

Particles motion is the same direction (parallel) to the direction of the wave

Describe transverse waves

Particles motion is perpendicular to waves motion

What type of wave is used in ultrasound

Longitudinal mechanical wave

Solids, liquids, gases support which type of wave?

Longitudinal (Best in solid and liquid) (Worst in gas)

Only solids support which type of wave?

Transverse

What is mode conversion?

One type of wave is converted into another form.

What is frequency? What is it’s units?

Cycles per second (number of complete variations an acoustic variable goes though in one second) Hz (Ultrasound uses MHz)

What is period? What is it’s units?

The time it takes for something to complete one cycle | Seconds - s Ultrasound it is measured in microseconds - us

What is a wavelength and what is it measured in?

Wavelength is the length of space one cycle takes to be completed Usually measured in millimetres - mm

If frequency increases what happens to period and wavelength?

If frequency increases the period and wavelength decrease

If period and wavelength increase what happens to frequency?

The frequency will decrease

What is propagation speed ?

Propagation speed (c) is the speed in which a wave moves through a medium

What is the average speed of sound through soft tissue?

1.54 mm/us 1540 m/s

What determines propagation speed?

The medium in which it travels through

What ways can strength of a wave be described?

Amplitude Intensity Power

What is amplitude?

The maximum displacement of an acoustic variable Strength of wave determined by source of sound (From middle of wave to crest or trough)

What is intensity?

A way to define the strength of a wave | Is concentration of energy in a sound beam

How is intensity and amplitude related? And what does it mean?

(I) is proportional to (Amp)squared A SMALL change in amplitude results in LARGE change in intensity

How is intensity related to power and area?

I = (P/A)

What does the relationship between intensity,power and area show?

Shows that as area increases, intensity decreases | Like a flashlight beam moved closer and further away from a surface

Intensity is not uniform in —— or ——, and we refer to intensities as these

Space and time

Describe space intensity

In sound beam the intensity is the greatest at the centre and fades towards outside. NOT UNIFORM

Describe time intensity.

Sound from the machines is sent in pulses (NO intensity during listening phase) Within a pulse the intensity starts off high at beginning and falls off

Space and time must be considered for——

Dose (how much energy is sent into patient) | Terminology used to assess bioeffects

The greatest intensity found across the beam is called the —— and is usually found at the centre.

Spatial peak (SP)

The average intensity measured over the entire beam is what ?

Spatial average (SA)

SP and SA are related by what?

Beam uniformity ratio (BUR)

What is the equation that relates the BUR, SP and SA

BUR = (SP / SA)

What is temporal peak? (TP)

The greatest intensity found in the pulse

The average for all values found in a pulse is called?

Pulse average (PA)

Can TP and PA be used interchangeably?

Yes they can, they are almost identical

This includes the dead time between pulses (listening phase), when there is no intensity.

Temporal average (TA)

TP and TA are related by what ?

Duty factor (DF)

What is the equation that relates TA, TP and DF

TA DF = —— TP

What is the highest intensity about sound beam

SPTP | Not realistic it happens too quick to be able to use it for anything

What intensity do we use for biological considerations.

SPTA | Highest intensity average over total experts expect time

What is lowest intensity about sound beam

SATA

To convert possible intensities from one to another use?

SP TA BUR = —— DF = —— SA TP

Consider SPTA the list the different modes of ultrasound from lowest to highest values.

``` Lowest M mode Real time-B mode Doppler Continuous wave (no dead time SPTP) Highest ```

SPTA values are dependent on ?

Depth (go deeper it changes shape of beam)

Velocities differ in different tissues, and this may result in —— appearing on the monitor

Artifacts

Propagation speed in fat

1460 m/s

Propagation speed in bone

4080 m/s

Does frequency change speed?

What is the range equation used to calculate?

Used to calculate the distance of a reflector from the probe

What is the range equation ?

D = C times t D is distance there and back C is the average speed of sound t is time there and back

What is the 1 cm rule

Another way to calculate the distance from the probe to the reflector (interface) Takes 13us to travel 1 cm there AND back

Can electromagnetic waves travel through space

Yes

What control on ultrasound machine can be adjusted to change the wavelength of the emitted sound?

You can adjust the frequency which will change the wavelength

What is the propagation speed for sound through air?

330 m/s

Out of 3 MHz, 5MHz, and 7MHz which has the best resolution? The best depth penetration?

3MHz for the best depth | 7MHz for the best resolution

Particle Motion & Wave Propagation Flashcards

(78 cards)